A fluorine-containing monomer such as a perfluoro(alkyl vinyl ether) is useful as a raw material monomer for heat resistant and chemical resistant fluororesins. For example, a perfluoro(alkyl vinyl ether) having carboxyl groups in its molecule, is useful as a raw material monomer for ion exchange membranes and can be produced via a diacyl fluoride (J. Fluorine Chem., 94, 65-68 (1999)).
Further, as a method for fluorinating all of C—H portions in a hydrocarbon compound to C—F, a method wherein fluorination is carried out by means of fluorine (elemental fluorine), or a method wherein fluorination is carried out by using, as a fluorine atom source, a product formed by electrolysis of hydrogen fluoride in an electrolyzer (i.e. a method so-called an electrochemical fluorination reaction), is known. Further, a gas phase method and a liquid phase method are known for the reaction employing fluorine.
Further, a method is also known wherein a perfluorinated ester compound having at least 16 carbon atoms, is pyrolyzed to obtain an acid fluoride compound. It is disclosed that an acid fluoride compound can be produced by a method wherein a hydrocarbon type ester compound having a corresponding carbon skeleton, is fluorinated by a liquid phase method employing fluorine gas (J. Am. Chem. Soc., 120, 7117 (1998)).
Further, as a common method for producing a diacyl fluoride, the following method employing iodine and fuming sulfuric acid, is known.CF2═CF2+I2→ICF2CF2IICF2CF2I+CF2═CF2→ICF2CF2CF2CF2IICF2CF2CF2CF2I+SO3→FCOCF2CF2COF
Further, a method is also disclosed wherein a diol diacetate containing no fluorine is used as the starting material, this material is directly fluorinated in 1,1,2-trichloro-1,2,2-trifluoroethane (hereinafter referred to as R-113) to produce a perfluorodiol diacetate, and then this is subjected to a dissociation reaction of the ester bond in pyridine to obtain a perfluorodiacyl compound and CF3COF (U.S. Pat. No. 5,466,877).
Further, a method is also proposed wherein CF2═CF— of a compound having CF2═CF— at one terminal and —COF at the other terminal, is halogenated with e.g. chlorine gas, and then, the other terminal is pyrolyzed to CF2═CF—, and further by dehalogenation, CF2═CF— is regenerated, to produce a compound having fluorinated vinyl groups at both terminals (JP-A-1-143843).
Further, a method for producing CF2═CFOCF2CF2CF═CF2 by pyrolysis of a potassium salt of a dicarboxylic acid such as KOCO(CF2)4OCF(CF3)CO2K, is reported (J. Org. Chem., 34, 1841 (1969)).
The electrochemical fluorination reaction has had a drawback such that an isomerization reaction, cleavage and re-bonding reactions of C—C bonds, etc. are likely to take place, whereby the intended compound can not be obtained in high purity. Further, there has been a problem that when reacted with fluorine in a gas phase, C—C single bonds undergo cleavage, whereby various types of by-products tend to be formed.
It is reported that the method of carrying out the reaction with fluorine in a liquid phase, is a method for solving the problems of the gas phase method (U.S. Pat. No. 5,093,432). As a solvent for the reaction to be used for this liquid phase method, a solvent capable of dissolving fluorine, is usually employed. However, a non-fluorinated type hydrocarbon compound or a hydrocarbon compound having a small fluorine content is hardly soluble in a solvent, whereby a problem has been observed such that the reaction will not proceed smoothly. Further, in a conventional liquid phase method, the reaction is carried out at a very low concentration, whereby there has been a problem that the production efficiency is poor, the reaction will be in a suspension system which is disadvantageous to the reaction. Further, there has been a problem that when the liquid phase method is applied to a low molecular weight hydrocarbon compound, the yield by the reaction tends to be very low.
Further, the conventional method for producing a diacyl fluoride has had a problem that the price of the raw material is high, and the method is economically disadvantageous. Further, iodine, fuming sulfuric acid, etc. are used, whereby there has been a problem that the apparatus is likely to be corroded, or handling of the reagent for the reaction tends to be difficult.
Further, in a case where a diol diacetate having no fluorine, is fluorinated in a liquid phase, there has been a problem that a decomposition reaction of the raw material substrate is observed. Further, the method of employing R-113 has a problem that such a method may not be used in future.
Further, the conventional method for producing a compound having fluorinated vinyl groups at both terminals has had a drawback such that two step reactions are required to form two fluorinated vinyl groups, and the substrate for the pyrolysis is hardly available and expensive.